The invention relates to a shaft sealing arrangement for a pump for delivering hot fluids. The shaft sealing arrangement is arranged in a housing and includes a dynamic shaft seal, in particular a slide ring seal, to seal a rotatable shaft relative to the housing, and a cooling ring which is mounted in front of the dynamic shaft seal in the direction of the pump interior and which surrounds the shaft at a small spacing.
Centrifugal pumps are normally used to deliver hot fluids. Such a pump includes a pump shaft fitted with impellers which is rotatably arranged in a housing, and dynamic shaft seals in order to seal the shaft towards the housing. Pumps for delivering hot fluids further contain cooling zones or stretches which are mounted in front of the dynamic shaft seals in the direction of the pump interior in order to lower the temperature so far that standard shaft seals can be used. In larger pumps such as in boiler feed pumps, mostly water-cooled cooling rings are found as the cooling zones which surround the shaft at a small spacing. The gap between the shaft and the cooling ring is dimensioned such that normally no contact takes place between the shaft and the cooling ring. The gap is thus sufficiently wide that an exchange of fluid can take place between the gap and the adjoining pump interior. As long as the shaft rotates, the cooling action of the cooling ring is constant over the periphery of the shaft. However, if the shaft is stationary, a thermal flow is formed in the gap between the shaft and the cooling ring by hot fluid rising into the upper part of the gap and cooled fluid falling into the lower part. This effect, which is known as the thermosyphon circulation, results in a curving of the shaft as a consequence of the irregular temperature distribution. As a result of this, the strain of the bearing parts, such as of the relief piston for the compensation of the axial pressure, increases and additional contact points occur between rotating and non-rotating parts of the pump. The start-up of the pump is thereby made more difficult and an increased wear of the affected pump parts results. To avoid the above-described thermosyphon circulation during the standstill of the pump, intermediate insulation spaces are provided in the cooling ring and at the shaft periphery. For example, so-called thermo-sleeves are attached to the shaft periphery; these are shaft protection sleeves with an air gap between the shaft and the sleeve. The intermediate insulation spaces, however, are frequently not sufficient to prevent the thermosyphon circulation.